This invention relates to a dropout compensation circuit for compensating for a dropped-out reproduction signal during the reproduction of a video signal.
A video tape recorder is known which is adapted to record and reproduce a video signal on a magnetic tape as a recording medium. Where the tape has scratches or dust particles on the surface, a video signal is not reproduced on that surface area of the tape, resulting in the dropout of a reproduction signal. If this occurs, image quality is degraded to a corresponding extent. Thus, a dropout compensation circuit is used to compensate for the dropout of the reproduction signal.
A conventional dropout compensation circuit permits the use of, in place of a dropped-out reproduction signal, the luminance signal component of a reproduction signal which is generated one horizontal scanning period prior to generation of the dropped-out reproduction signal. To obtain a better image quality, a signal including, not only a luminance signal component, but a chrominance signal component, must be used in place of the dropped-out reproduction signal.
To record more image signals per unit length on the tape of a home video tape recorder, the video tracks are mutually adjacently arranged without providing any guide band between the video tracks. The video signal recorded on the adjacent tracks is sequentially reproduced through two video heads. Where a video signal recorded on a certain video track is to be reproduced, the portion of the video signal recorded on the adjacent video track is also reproduced, causing the corresponding partial reproduction signal to be mixed, as a crosstalk component, with the main reproduction signal. However, in the luminance signal present in the high frequency region, no crosstalk occurs due to the azimuth loss. In the home video tape recorder, it is necessary to eliminate the crosstalk component mixed with the chrominance signal. For example, a phase inverting (PI) method is adopted in a .beta.-system video tape recorder, while a phase shifting (PS) method is adopted in a VHS-system video tape recorder.
In the PI method, a video signal is recorded on the corresponding video track through one of two video heads in such a way that the phase of the chrominance signal is inverted for each horizontal scanning period. The video signal is recorded on the adjacent video track through the other video head such a way that the phase of the chrominance signal is not inverted. In the PS method, a video signal is recorded on the corresponding video track through one of two video heads in such a way that the phase of the chrominance signal is, for example, lagged by 90.degree. for each horizontal scanning period. The video signal is recorded on the adjacent video track through the other video head in such a way that the phase of the chrominance signal is lead by 90.degree. for each horizontal scanning period.
Where a chrominance signal recorded by the PI method or the PS method is to be reproduced, the reproduction chrominance signal is so processed that the chrominance signal may be given the same phase for each horizontal scanning period on the same video track. The crosstalk component included in the chrominance signal for each horizontal scanning period has a phase inverted for each horizontal scanning period. When a chrominance signal recorded by the PI method and PS method is reproduced, if a chrominance signal included one horizontal period prior to generation of a present chrominance signal is used in the same manner as the compensation of the luminance signal, to compensate for a dropped-out reproduction signal, a crosstalk component will be mixed into the present reproduction signal.